A reduction in reflection of light applied from an external light source and an enhancement in the visibility of image are required of an image display face in image display devices such as liquid crystal displays (LCDs) or cathode ray tube display devices (CRTs). On the other hand, it is common practice to reduce the reflection from the image display face in the image display device and thus to improve the visibility by utilizing an optical laminate (for example, an antireflection laminate) comprising an antireflection layer provided on a light transparent base material.
The prevention of lowered contrast and lowered visibility caused by external light reflection or image reflection is required of image display devices, for example, cathode ray tube display devices (CRTs), plasma displays (PDPs), organic or inorganic electroluminescent displays (ELDs), field emission displays (FEDs), or liquid crystal displays (LCDs). Accordingly, it is common practice to provide an antireflection laminate on the outermost surface of an image display device from the viewpoint of reducing image reflection or reflectance using the principle of light scattering or the principle of optical interference.
Further, it has hitherto been pointed out that the outermost surface of the optical laminate is exposed to various service environments and thus is likely to be scratched and contaminated. To overcome this drawback, Japanese Patent Laid-Open No. 104403/1998 proposes an optical laminate comprising a hard coat layer in which a contamination preventive agent has been added to the hard coat layer from the viewpoint of improving the scratch resistance and contamination prevention of the image display face.
So far as the present inventors know, however, up to now, any optical laminate comprising a light transparent base material and a low-refractive index layer, provided on the light transparent base material, which can simultaneously realize contamination preventive properties and slipperiness, has not been proposed.
At the time of the present invention, the present inventors have found that a low-refractive index layer, which can simultaneously realize contamination preventive properties and slipperiness, can be formed, when the low-refractive index layer contains a contamination preventive agent and/or a slipperiness imparting agent and, at the same time, the contamination preventive agent and/or the slipperiness imparting agent are added so that the concentrations of the contamination preventive agent and/or slipperiness imparting agent have a gradient from the surface of the hard coat layer toward the surface of the low-refractive index layer. Accordingly, the present invention provides an optical laminate comprising a low-refractive index layer having both contamination preventive properties and slipperiness.
Thus, according to the present invention, there is provided an optical laminate comprising a light transparent base material, and a hard coat layer and a low-refractive index layer provided in that order on the light transparent base material, wherein
the low-refractive index layer has a refractive index of not more than 1.45,
the low-refractive index layer contains a contamination preventive agent and/or a slipperiness imparting agent, and
the contamination preventive agent and/or slipperiness imparting agent are added so that the concentrations of the contamination preventive agent and/or slipperiness imparting agent are increased from the surface of the hard coat layer toward the surface of the low-refractive index layer.